1. Field of the Invention
The present invention relates to an apparatus and a method for producing trichlorosilane, which converts tetrachlorosilane into trichlorosilane.
Priority is claimed on Japanese Patent Application No. 2009-057654, filed on Mar. 11, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
High-purity polycrystalline silicon (Si) is produced by the hydrogen reduction reaction (Equation (2)) and the thermal decomposition reaction (Equation (3)) of highly purified trichlorosilane (SiHCl3), which is produced by the conversion reaction (Equation (1)) of tetrachlorosilane (SiCl4) with hydrogen.SiCl4+H2→SiHCl3+HCl   (1)SiHCl3+H2→Si+3HCl   (2)4SiHCl3→Si+3SiCl4+2H2   (3)
As an apparatus for producing trichlorosilane using the reaction represented by Equation (1), for example, a conversion reaction apparatus, which is described in Japanese Patent No. 3781439, has been disclosed. Trichlorosilane is recovered from the reaction product gas produced in a reaction chamber (converter reactor) in the conversion reaction apparatus. The reaction chamber (converter reactor) surrounded by a heating element has a double chamber structure made of an outer chamber and an inner chamber configured by two tubes concentrically arranged. A raw material feeding tube line, which supplies hydrogen and tetrachlorosilane to the reaction chamber, and a discharge tube line, through which the reaction product gas is discharged from the reaction chamber, are connected to the reaction chamber via a heat exchanger below. In the heat exchanger, heat is exchanged between the reaction product gas discharged from the reaction chamber and the raw material gas fed to the reaction chamber. As a result, the raw material gas is pre-heated and the reaction product gas is cooled.
In Japanese Examined Patent Application Publication No. S57-38524, a method, in which tetrachlorosilane and hydrogen are introduced to a reaction chamber and are subjected to the conversion reaction at a temperature of 600 to 1,200° C. to obtain a reaction product gas containing trichlorosilane and hydrogen chloride, and the reaction product gas discharged from the reaction chamber is rapidly cooled at a cooling rate such that 300° C. or less can be reached within 1 second, was disclosed.
In an apparatus for producing trichlorosilane disclosed in Japanese Patent No. 3781439, a reaction product gas is cooled by heat exchange with a raw material gas in a heat exchanger on a lower portion of a reaction chamber. When the cooling rate is too low, during a process of cooling the reaction product gas, Equation 4, which is the reverse reaction of Equation (1), occurs, and the conversion ratio to trichlorosilane is decreased.
Japanese Examined Patent Application Publication No. S57-38524 disclosed a solution for the problem. The reaction of Equation (4) was suppressed by rapidly cooling the reaction product gas to a temperature range of equal to or less than 300° C. in less than 1 second. However, when a cooling rate, at which the reaction product gas is cooled, is too fast, dichlorosilylene (SiCl2) contained in the reaction product gas reacts with tetrachlorosilane to produce polymers as byproducts (Equation (5)). Generation of the polymers reduces the conversion ratio to trichlorosilane and causes clogging of tubes due to deposition of the polymers inside tubes.SiHCl3HCl→SiCl4+H2   (4)SiCl2+SiCl4→Si2Cl6   (5)
During the conversion reaction, a large amount of dichlorosilylene is produced at a high temperature (particularly at a temperature above 1200° C.) and discharged from the converter reactor with the reaction product gas. The polymers mentioned here collectively refer to high-order chlorosilanes with two or more silicon atoms, such as, hexachlorodisilane (Si2Cl6), octachlorotrisilane (Si3Cl8), or tetrachlorodisilane (Si2H2Cl4).
As described above, when the reaction product gas is rapidly cooled for an extremely short time, the reaction converting trichlorosilane to tetrachlorosilane (Equation (4)) during cooling is suppressed, so that a recovery ratio of trichlorosilane is increased. On the other hand, when a temperature after cooling is too low, polymer production is increased (Equation (5)), and consequently the problematic polymer deposition occurs in the tubes after the cooling process. When the cooling rate is too slow, the recovery ratio of trichlorosilane is reduced since the reaction converting trichlorosilane to tetrachlorosilane proceeds faster, even though the polymer production can be suppressed easier by maintaining a proper temperature after cooling.
Therefore, the reaction product gas discharged from the converter reactor has to be cooled at a properly regulated rate, especially in a high temperature range of greater than or equal to 600° C., in which trichlorosilane is likely to decompose. However, the temperature of the reaction product gas discharged from the converter reactor is extremely high (greater than or equal to 1000° C.), and therefore it is difficult to perform rapid cooling at a properly regulated rate in the temperature range of greater equal to or higher than 600° C. Under these circumstances, conventionally, increasing the recovery ratio of trichlorosilane has been given priority, cooling the reaction product gas at an excessive cooling rate. As a result, the formation of the polymers has been a problem in the trichlorosilane production process.